Aromatic oligomers and resins

ABSTRACT

Compositions comprising an oligomer which (a) comprises the repeating unit (Ar - CHR), and where Ar is an aromatic group and R is hydrogen or a hydrocarbyl group or hydrogen, (b) has pendant and/or terminal groups which include inter alia acyloxymethyl, hydroxymethyl and carboxyl, and (c) has a functionality between 0.5 and 10, and processes for the preparation thereof are described. These compositions may be used in dental, electrical and electronic applications.

This is a division, of application Ser. No. 558,525, filed Dec. 6, 1983,now U.S. Pat. No. 4,530,992, issued 7/23/85.

This invention relates to aromatic oligomers, to the preparationthereof, to resins prepared from compositions which comprise theoligomers and to filled and/or fibre-reinforced articles of the resins.

The reaction of diphenyl oxide, diphenyl sulphide, dibenzofuran anddibenzothiophene with formaldehyde in the presence of a carboxylic acidand catalytic quantities of a strong acid at reflux temperatures to giveoligomers are known, for example as described in U.S. Pat. No.3,914,194.

We have now found that where the molar ratio of strong acid to aromaticcompound is at least 1:1 (a) the aforesaid reaction affords noveloligomers, (b) certain aromatic compounds which are less reactive thanthe aforesaid aromatic compounds can be used, and (c), where thecarboxylic acid is an olefinically unsaturated carboxylic acid which ispolymerisable by addition polymerisation (hereinafter referred to forconvenience as "polymerisable olefinically unsaturated carboxylic acid")the reaction can be carried out at temperatures below 90° C. usingcommercially available grades of a polymerisable olefinicallyunsaturated carboxylic acid, which grades contain conventional amountsof stabiliser, often without the addition of further quantities ofstabiliser. The presence of further quantities of stabiliser wouldreduce the ease with which such oligomers may be cured.

Compositions comprising the aforesaid oligomers may be converted intocured resins, either directly or via conversion into reactiveintermediates. For example, where the pendant and/or terminal groups areacyloxymethyl groups in which the acyl portion is derived from apolymerisable olefinically unsaturated carboxylic acid curing may beeffected in the presence of a suitable addition polymerisationinitiator; where the pendant and/or terminal groups are acyloxymethylgroups in which the acyl portion is derived from an aromatic oraliphatic carboxylic acid curing may be effected by a suitable strongacid. The preparation and use of reactive intermediates is more fullydescribed hereinafter. By careful selection of the structural featuresof the oligomers, cured resins having good combination of properties maybe produced. The cured resins may provide the matrix for filled and/orfibre reinforced composites.

According to a first aspect of the present invention there is provided acomposition comprising an oligomer, which may be linear or branched,which comprises the repeating unit

    --Ar.sup.1 --CHR--

and which has pendant and/or terminal groups, which groups, which may bethe same or different, are acyloxymethyl, hydroxymethyl, carboxyl,##STR1## wherein Ar¹ is an aromatic group, or a substituted derivativethereof, each of which may be the same or different; R, each of whichmay be the same or different, is hydrogen, or a hydrocarbyl group andthe average number of pendant and/or terminal groups, as hereinbeforedefined, on each oligomer molecule (hereinafter referred to forconvenience as "functionality") has a value between 0.5 and 10, with theproviso that where the aromatic group is a diphenyl oxide, diphenylsulphide, dibenzofuran or dibenzothiophene residue, R is hydrogen andthe pendant and/or terminal groups are acyloxymethyl and/orhydroxymethyl then the ratio of methylene groups which are attached totwo aromatic groups at positions para to the heteroatoms in botharomatic groups (hereinafter referred to for convenience as "para-paralinkages") to methylene groups which are attached to two aromatic groupsat a position ortho to the heteroatom in one of the aromatic groups andat a position para to the heteroatom in the other aromatic group(hereinafter referred to for convenience as "ortho-para linkages") isless than 5:1.

In oligomers of which compositions according to the first aspect of thepresent invention are comprised the aforesaid ratio is preferablybetween 5:1 and 2:1. Oligomers having such ratios have less tendancy tocrystallise than oligomers known in the art.

The aforesaid ratio may be determined by quantitative C¹³ -nuclearmagnetic resonance spectroscopy in which para-para linkages generate asignal at about 40 ppm and the ortho-para linkages generate a signal atabout 35 ppm.

According to a second aspect of the present invention there is provideda process for the preparation of oligomers of which the compositionsaccording to the first aspect of the present invention are comprisedwhich process comprises at least the step of reacting an aromaticcompound, an aldehyde and a carboxylic acid in the presence of a strongacid characterised in that the molar ratio of strong acid to aromaticcompound is at least 1:1, with the proviso that where the carboxylicacid is a polymerisable olefinically unsaturated carboxylic acid thereaction is carried out at a temperature below 90° C.

In linear oligomers of which the compositions according to the firstaspect of the present invention may be comprised it will be appreciatedthat each aromatic group may be bound into the oligomer backbone bybonds which may be ortho or para to each other. For example, where thearomatic group is derived from diphenyl oxide, backbone linkages such as##STR2## may be present.

The aromatic groups in an oligomer of which a composition according tothe first aspect of the present invention is comprised may bemono-nuclear, e.g. as in phenylene; fused polynuclear, e.g. as innaphthalene or anthracene; or preferably have the structure --φ--Y¹--φ--. In --φ--Y¹ --φ--, φ is the phenylene group and Y¹ is a directlink between the two phenylene groups; a divalent residue which includesone or more in-chain atoms, each of which atoms may be carbon or ahetero atom and may have one or more atoms appendant thereto, e.g.--O--, --S--, --CH₂ -- or a substituted derivative of --CH₂ --, e.g.--C(CH₃)₂ --; --CH₂ CH₂ --, and ##STR3## where Y², which may be the sameor different, is a group which activates the aromatic nucleus toelectrophilic attack, e.g. --O-- and --S--, and Y³ is a group whichdeactivates the aromatic nucleus to electrophilic attack, e.g. --SO₂ --and --CO--.

Substituents which may be present on the aromatic groups include interalia lower alkyl groups having up to five carbon atoms, e.g. methyl andethyl; lower alkoxy groups e.g. methoxy; and halo groups, e.g. chloro.

Where the group R in the repeating unit --(Ar¹ --CHR)-- is a hydrocarbylgroup it may be an aryl group, e.g. phenyl; an alkaryl group, e.g.tolyl; an aralkyl group, e.g. benzyl; or preferably an alkyl grouphaving up to six carbon atoms, e.g. methyl or ethyl. We do not excludethe possibility that R may have one or more suitable substituents, e.g.halo groups. Preferably, however, R is a hydrogen atom.

Where the pendant and/or terminal groups on an oligomer of which thecomposition according to the first aspect of the present invention iscomprised are acyloxymethyl groups the acyl portion thereof may bederived from inter alia an aliphatic carboxylic acid, an aromaticcarboxylic acid, or preferably a polymerisable olefinically unsaturatedcarboxylic acid or a substituted derivative thereof. Where the acylportion is derived from an aliphatic carboxylic acid or an aromaticcarboxylic acid such oligomers have a slow rate of cure and liberateproducts which are volatile and/or toxic and/or corrosive and oftendifficult to remove completely; to obtain resins therefrom of highsoftening point, say above 100° C., high functionality oligomers areneeded which, during curing, generate more byproducts, shrink, and tendto form voids and give brittle products.

As examples of suitable aliphatic and aromatic carboxylic acids fromwhich the aforesaid acyloxymethyl groups may be derived may be mentionedformic, acetic, propionic, hexanoic, benzoic, and haloacetic, e.g.dichloroacetic, acids. Whilst it may be commercially attractive toemploy an inexpensive carboxylic acid, e.g. acetic acid, it may bedesirable, for example where the oligomer is to be used for theproduction of a substantially three-dimensional article to use arelatively involatile acid, for example having up to about eighteencarbon atoms, because in the curing of such an oligomer less pressure isrequired to overcome the problem of void formation during in-mouldcuring. Additionally, it will be appreciated that where a volatilecarboxylic acid is evolved it is often preferred that it is not anoxious product such as dichloroacetic or trifluoroacetic acid.

As examples of suitable olefinically unsaturated carboxylic acids fromwhich the aforesaid acyloxymethyl groups may be derived may be mentionedethacrylic, crotonic, angelic, cinnamic, maleic, oleic and linoleicacids or preferably acrylic or methacrylic acid.

It will be appreciated that the functionality of oligomers of which thecompositions according to the first aspect of the present invention arecomprised will affect inter alia the viscosity and softening point ofthe oligomers and the mechanical properties of the cured resins preparedtherefrom. It is often preferred that the functionality is between twoand six. For example, where it is desired that a cured resin preparedfrom a composition according to the first aspect of the presentinvention has a softening point of at least 200° C. and the oligomer ofwhich the composition is comprised has a number average molecular weightof about 1000, the oligomer preferably has a functionality of at leastfour; such cured resins are often able to withstand flash exposure, sayof the order of a few minutes, to temperatures of about 270° C. It willbe appreciated that where the molecular weight of the oligomer isgreater or less than 1000 the functionality thereof has to be increasedor decreased respectively t give a cured resin of softening point atleast 200° C. The skilled man by simple experiment will be able todetermine satisfactory number average molecular weight/functionalitycombinations for the oligomers.

As the number average molecular weight of an oligomer of whichcompositions according to the first aspect of the present invention arecomprised increases, the viscosity of the oligomer increases and itbecomes a viscous gum and then a solid. Above a number average molecularweight of about 1000, cohesive, tack-free films of oligomer can beobtained. Furthermore we have found that cohesive, tack-free films canbe prepared from oligomers which have a number average molecular weightof less than about 1000 by dissolving therein certain polymers, i.e.so-called "polymeric binders", e.g. polystyrene, polyvinyl pyrrolidone,polyvinyl butyral, polyvinyl acetate, or polymethylmethacrylate or apolymer of the general formula

    --[Ar.sup.1 --CHR].sub.m --                                I

where Ar¹ and R have the meaning hereinbefore ascribed to them and m issuch that the number average molecular weight of the polymer of generalformula II is more than 3000.

The aromatic compound used in the process according to the second aspectof the present invention may be mononuclear, e.g. as in benzene; fusedpolynuclear, e.g. as in naphthalene or anthracene; or preferably Ph--Y¹--Ph in which Ph is the phenyl group and Y¹ has the meaning hereinbeforeascribed to it. The aromatic compound may have substituents ashereinbefore described.

As examples of aldehydes which may be used in the process according tothe second aspect of the present invention may be mentioned inter aliabenzaldehyde, tolualdehyde, phenylacetaldehyde or preferably a loweralkyl aldehyde, e.g. acetaldehyde and propionaldehyde, more preferably,however, the aldehyde is formaldehyde.

Whilst we do not exclude the possibility that a solution of formaldehydein, for example, water or methanol, may be used in the process accordingto the second aspect of the present invention, preferably theformaldehyde is in a solid form, e.g. paraformaldehyde, form or morepreferably trioxane.

The carboxylic acid used in the process of the second aspect of thepresent invention is a hydrocarbyl carboxylic acid, which hydrocarbylgroup may have one or more substituents and may be an alkyl, aryl,alkaryl, aralkyl or preferably an alkylene group. Examples of suitablecarboxylic acids have been hereinbefore described. We have found that asthe strength of the carboxylic acid is increased, e.g. dichloroaceticacid or trifluoroacetic acid, the reaction rate of the process isincreased.

Where the carboxylic acid is methacrylic acid we have found that whereit contains more than 500 ppm of methacrylamide there is a tendency forgelation and/or emulsification of the reaction mixture to occur whencarrying out the process according to the second aspect of the presentinvention.

The strong acids used in the process according to the second aspect ofthe present invention have pKa's of less than 0.5.

As examples of strong acids which may be used in the process accordingto the second aspect of the present invention may be mentioned interalia phosphoric acid, p-toluenesulphonic acid, trifluoromethanesulphonic acid, dichloroacetic acid, trifluoroacetic acid or preferablysulphuric acid. It will be appreciated that where the carboxylic acidused in the reaction is a strong acid as hereinbefore defined a portionthereof may serve as the strong acid.

In the process according to the second aspect of the present invention 1mole of an aromatic compound is treated with about 1.0 to 15 moles of analdehyde, about 5 to 40 moles of a carboxylic acid, and about 1 to 20moles of strong acid. If too much strong acid is used it is difficult tocontrol the exotherm and gelation occurs.

The reaction mixture used in the process of the present invention mayinclude water. The water may be added as a discrete component of thereaction mixture or, where one of the reactants in the reaction mixtureis used in the form of an aqueous solution, e.g. formalin and 85%sulphuric acid, at least a portion of the water is added as the solventin the solution. The total amount of water added to the reaction mixtureis typically less than 100 moles per mole of the aromatic compound.

Preferably the molar ratios of aromatic compound:aldehyde:carboxylicacid:strong acid:water which are used in the process of the presentinvention are 1:2-10:5-15:1-10:2-30 such ratios tend to decreasepara-para:ortho-para ratio.

Conveniently the aromatic compound may be added to a mixture of theother reactants or the aldehyde may be added to a mixture of the otherreactants.

A suitable inert diluent, e.g. 1,2-dichloroethane, or dioxan, may bepresent in the reaction mixture to increase the solubility of thearomatic compound therein. There is a tendancy for such reactionmixtures to emulsify and hence the presence of a suitable inert diluentis often not preferred.

Where no inert diluent is present the process according to the secondaspect of the present invention is preferably carried out between 50° C.and 90° C., more preferably at a temperature between 60° C. and 80° C.

The process according to the second aspect of the present invention maybe carried out for between five minutes and twenty-four hours. Oftensubstantially all the aromatic compound has reacted within a few hours.

Oligomers of which compositions according to the present invention arecomprised may contain in-chain --OCHR-- groups. Where it is desired toreduce, at least, the number of in-chain --OCHR-- groups, the reactionmay be continued for an extended period of time, e.g. up to, say, about24 hours, and/or the ratios of aromatic compound:aldehyde:carboxylicacid:strong acid:water used in the reaction are 1:2-5:5-8:1-5:2-0. WhereR is hydrogen the presence of in-chain --OCH₂ -- is indicated by thepresence of one or more signals in the C¹³ -nuclear magnetic resonancespectrum of the oligomer.

When reaction is judged to be complete the product is treated to removeat least substantially all the strong acid, particularly where apolymerisable olefinically unsaturated acid is used in the process. Thepresence of residual strong acid can lead to the production ofundesirable side products, with consequent decrease in properties,during production of a cured resin from the oligomer. Removal of thestrong acid is conveniently effected by separating the inorganic phasefrom the organic phase and washing the organic phase with water,preferably hot water, a weakly alkaline solution, e.g. sodiumbicarbonate, and then water.

An oligomer of which a composition according to the first aspect of thepresent invention may be comprised which has pendant and/or terminalhydroxymethyl groups may be prepared by hydrolysis of an appropriateoligomer in which the pendant and/or terminal groups are acyloxymethylgroups. Preferably hydrolysis is effected under basic conditions.

An aligomer of which a composition according to the first aspect of thepresent invention is comprised which has pendant and/or terminalcarboxylic groups may be prepared by oxidation, with a suitableoxidising agent, e.g. chromic acid or potassium permanganate, of anappropriate oligomer which has one or more pendant and/or terminalacyloxymethyl or hydroxymethyl groups. Where the oligomer which is to beoxidised has at least one methylene group in the backbone thereof theoxidising agent is preferably strong enough to oxidise the at least onemethylene group to at least one keto group and more preferably ispotassium permanganate; cured resins prepared from oligomers within-chain keto groups instead of in-chain methylene groups or more stablethermally.

An oligomer of which a composition according to the first aspect of thepresent invention is comprised which has pendant and/or terminal##STR4## groups may be prepared by reacting an appropriate oligomerwhich has pendant and/or terminal acyloxymethyl or hydroxymethyl groupswith an excess of o-xylene and Lewis acid catalyst, e.g. BF₃, to form anoligomer which has pendant and/or terminal ##STR5## groups, the methylgroups of which may be oxidised with a suitable oxidising agent, e.g.potassium permanganate to form a group ##STR6##

An oligomer of which a composition according to the first aspect of thepresent invention is comprised which has pendant and/or terminal##STR7## groups may be prepared by reacting an appropriate oligomerwhich has pendant and/or terminal hydroxymethyl and/or acyloxymethylgroups with a phenol. Typically the reaction is carried out by heatingthe oligomer which has pendant and/or terminal acyloxymethyl and/orhydroxymethyl groups with one or more molar equivalents of a phenol foreach acyloxymethyl or hydroxymethyl group present in the presence of asuitable catalyst, e.g. toluene-sulphonic acid.

An oligomer of which a composition according to the first aspect of thepresent invention is comprised which has pendant and/or terminal##STR8## groups may be prepared by reacting an appropriate oligomerwhich has pendant and/or terminal hydroxymethyl groups with an aniline.Typically the reaction is carried out by heating the oligomer which haspendant and/or terminal hydroxymethyl groups with one or more molarequivalents of an aniline for each hydroxylmethyl group present.

Where oligomers of which compositions according to the first aspect ofthe present invention are comprised have pendant and/or terminalacyloxymethyl groups in which the acyl group is derived from apolymerisable olefinically unsaturated carboxylic acid they may becopolymerised with a suitable polymerisable olefinically unsaturatedcomonomer, e.g. an acrylate or methacrylate, or where the oligomer is aliquid, homopolymerised. Polymerisation may be effected by any of thetechniques conventionally used in the addition polymerisation ofpolymerisable olefinically unsaturated monomers. However, free radicalinitiation is preferred. Application of heat may assist thepolymerisation although by suitable choice of catalyst it is possible toeffect polymerisation at or near ambient temperature. Vinyl comonomerswhich may be used in admixture and with which the oligomers may becopolymerised include vinyl esters, aromatic vinyl compounds and vinylnitriles.

Suitable vinyl esters include, for example, vinyl acetate and esters ofacrylic and methacrylic acids, which esters may have one or more estergroups, e.g. methyl, cyclohexyl, n-hexyl, and tetrahydrofurfurylacrylates and methacrylates, ethylene glycol acrylate and methacrylate,di- and triethylene glycol acrylates and methacrylates, andpentaerythritol triacrylate. As examples of suitable aromatic vinylcompounds may be mentioned inter alia styrene and derivatives thereof,e.g. alpha-methyl styrene, and vinyl toluene. Suitable vinyl nitrilecompounds include inter alia acrylonitirle and derivatives thereof, e.g.methacrylonitrile.

Where a polymerisable olefinically unsaturated comonomer is present inthe composition it typically provides between 5 and 95% by weight of thecomposition. The quantity of polymerisable olefinically unsaturatedcomonomer which is used will depend on inter alia the viscosity which isrequired and on the mechanical properties required in the cured resinprepared therefrom.

Compositions according to the first aspect of the present invention,particularly those which comprise an oligomer which has pendant and/orterminal acyloxymethyl groups in which the acyl group is derived from apolymerisable olefinically unsaturated carboxylic acid, are often highlyresistant to aggressively corrosive environments, e.g. pH 12° at 80° C.for 24 hours and chromic acid at 60° C. for 30 minutes, and may find usein a variety of applications.

Such compositions when filled with one or more suitable particulatefillers, e.g. a borosilicate glass powder of silica powder, to asuitable level, typically 30-92% w/w of filler, have properties, e.g.low water uptake, low level of ionic impurities, high softening point,low shrinkage and good tracking resistance. They may be used as dentalmaterials, for example as unfilled sealants, adhesives, bonding agentsand glazes, or, where filled with a particulate filler, e.g. glassparticles, as artificial teeth or dental fillings. They may be used inelectronic or electrical applications, for example in photoresists, e.g.non-strippable dry film resists, in solder masks and, when filled, asencapsulants. They may be used in reprographic processes, e.g. in thepreparation of printing plates. They may be used as abrasion resistantsurface coatings, particularly when in admixture with a particulatefiller.

Where compositions according to the first aspect of the presentinvention are used in or as dental materials, curing thereof ispreferably effected by a visible light curing technique using aphoto-initiator system, for example as disclosed in British PatentSpecification No. 1408265, or preferably in European Patent PublicationNo. 59649A, the disclosure in which publication is incorporated hereinby way of reference. Such compositions are particularly useful as thematrix in visible light cured radio-opaque dental filling materials.Where they are used in dental filling materials a copolymerisablecomonomer may be present and the ratio of oligomer to comonomer may bechosen to give a refractive index equal to the refractive index of thefiller, thus rendering the composition substantially transparent to thecuring radiation and hence increasing the depth of cure. Where they areused in dental filling materials it will be appreciated that the weightratios of oligomer:copolymerisable comonomer, where present:particulatefiller is such that the material is a viscous fluid, that is paste-likeand not powdery or crumbly at ambient temperatures, so that in theuncured state it may be shaped in a coherent mass and will maintain thatshape without substantial flow; typically such weight ratios lie in therange 2-3:1-2:20-22. Such characteristics will enable the composition tobe inserted into a substantially vertical cavity in or mould on a toothin the upper jaw without deformation before cure.

Accordingly, a third aspect of the present invention provides a fluiddental filling material which comprises (a) at least one oligomer whichis derived from an aromatic compound and an aldehyde and which haspendant and/or terminal acyl-oxymethyl groups in which the acyl group isderived from a polymerisable olefinically unsaturated carboxylic acid,which oligomer is preferably as defined in the first aspect of thepresent invention, and (b) a particulate filler.

The oligomer used in the third aspect of the present inventionpreferably has a functionality of between 2 and 5 and a number averagemolecular weight of between 500 and 1000.

Where a composition according to the first aspect of the presentinvention which comprises an oligomer in which the pendant and/orterminal groups comprise acyloxymethyl groups in which the acyl group isderived from an olefinically unsaturated carboxylic acid are used asreprographic materials, curing is effected by a photo curing technique,for example using the photoinitiator compositions described in ourEuropean Patent Publication No. 90493A, and a suitable low-powered laserbeam, e.g. from an argon source. We have found that such compositionsmay be gelled in a few one-thousandths of a second and may be used as socalled "camera speed resists". Such resists may be used in theproduction of printed circuits, letterpress printing plates (where theprint is in relief) and lithographic printing plates (where the plate isessentially planar and has both oleophilic, ink receptive areas, andhydrophilic, ink-repellent areas). The oligomer used in suchapplications preferably has a functionality of at least four.

Accordingly a fourth aspect of the present invention provides a cameraspeed resist comprising (i) a polymerisable composition which comprisesat least one oligomer which (a) is derived from an aromatic compound andan aldehyde and (b) has pendant and/or terminal acyloxy-methyl groups inwhich the acyl group is derived from a polymerisable olefinicallyunsaturated carboxylic acid, which oligomer is preferably as defined inthe first aspect of the present invention, and (ii) a photoinitiatorcomposition.

In an often preferred method of use, a camera speed resist of the fourthaspect of the present invention is typically coated on a conventionallithographic plate. The resist is then polymerised at those points wherea permanent image is not required. The unpolymerised regions of theresist are dissolved in a suitable solvent to leave one or more exposedregions of the plate on which a metal, e.g. copper or nickel, issubsequently deposited, electrolytically or electrolessly. Afterdeposition of the metal, the polymerised portions of the resist areremoved.

Compositions according to the first aspect of the present inventioncomprising an oligomer which (a) has pendant and/or terminal groupswhich are acyloxymethyl groups in which the acyl group is derived from apolymerisable olefinically unsaturated carboxylic acid, and (b) has afunctionality of at least three may be mixed with a photosensitivepolymerisation initiator and formed into a cohesive tack-free film,either directly or, particularly where the number average molecularweight of the oligomer is less than 1000, after admixture therewith of aso-called polymeric binder as hereinbefore described. Such a film may beused as a so-called non-strippable or permanent dry film resist.

Accordingly a fifth aspect of the present invention provides aphotopolymerisable composition which comprises (a) a polymerisablecomposition which comprises at least one oligomer which (i) is derivedfrom an aromatic compound and an aldehyde and (ii) has pendant and/orterminal acyloxy methyl groups in which the acyl group is derived froman olefinically unsaturated carboxylic acid and has a functionality ofat least three, which oligomer is preferably as defined in the firstaspect of the present invention, and (b) a photo-sensitive initiator.

For use as a permanent dry film resist a photopolymerisable compositionaccording to the fifth aspect of the present invention is firstlyconverted into a film. Conveniently the film is formed by casting from asolution in a suitable volatile solvent, e.g. methyl ethyl ketone.Typically the film is formed between a support film and a cover film towhich the oligomer does not adhere and which do not soften or undulydisorientate, where orientation is present therein, during thefilm-forming process. Often the cover film is polyethylene and thesupport film is polyethylene terephthalate. Typically a permanent dryfilm resist formed from a photopolymerisable composition of the fifthaspect of the present invention has a thickness in the range 5 to 100microns, although it will be appreciated that the thickness of the filmwill depend on the particular application for which it is to be used.

The cover film, typically a polyethylene film, is removed to expose onesurface of the film of the photopolymerisable composition of the fifthaspect the present invention. The said exposed surface is brought intocontact with a surface of a circuit board, e.g. a glass-fibre reinforcedepoxy, on which the printed circuit is to be carried. The film is bondedto the circuit board, preferably by the application of mild heat andpressure thereto, although we do not exclude the possibility that asuitable bonding aid and/or adhesive may be employed.

Certain defined portion(s) of the film of the photopolymerisablecomposition of the fifth aspect of the present invention is/aresubjected to suitable electromagnetic radiation, typically a radiationwhich is conventionally employed in manufacturing processes in theelectronics industry, e.g. with a peak output in the range 300 to 500nanometers, which initiates polymerisation of the photopolymerisablecomposition to form a film of cured resin. The support film is removedand then the unpolymerised portions of the photopolymerisablecomposition are removed to expose one or more portions of the circuitboard. The circuit board is then subjected to further processingtechniques, in which a conductive layer, e.g. copper is deposited on thesaid exposed portions, with no undue deleterious effect on the film ofcured resin.

Where a solder mask comprises a composition according to the firstaspect of the present invention it is preferably used in the form of acoherent tackfree or solid film, one surface of which is in contact witha suitable support film, and one surface of which is in contact with acover film.

Polymerisable compositions according to the first aspect of the presentinvention in which the pendant and/or terminal groups on the oligomerare acyloxymethyl groups in which the acyl residue is derived from asaturated aliphatic carboxylic acid or an aromatic carboxylic acidand/or a substituted derivative thereof may be cured under suitableconditions to give resins having useful properties, e.g. glasstransition temperatures in the range 80° C. to 290° C., depending on thefunctionality and molecular weight of the oligomer. Moreover, the resinsmay form the matrices for useful fibre-reinforced composites,particularly where the fibre is carbon fibre.

Accordingly, a sixth aspect of the present invention provides curedresins, and composites thereof, formed by curing a composition whichcomprises an oligomer which (a) is derived from an aromatic compound andan aldehyde and (b) has pendant and/or terminal acyloxymethyl groups inwhich the acyl group is derived from a saturated aliphatic carboxylicacid, or an aromatic carboxylic acid, or a substituted derivativethereof which oligomer is preferably as defined in the first aspect ofthe present invention.

Curing of an oligomer which has pendant and/or terminal groups which areacyloxymethyl groups the acyl group of which is derived from a saturatedaliphatic carboxylic acid or an aromatic carboxylic acid or asubstituted derivative thereof may be effected by heating the oligomer,typically up to about 80° to 140° C., preferably in the presence of asuitable catalyst, e.g. boron trifluoride etherate. Alternatively,particularly where the oligomer is in the form of a film or sheet, itmay be irradiated with suitable electromagnetic radiation in thepresence of a compound which interacts with the electromagneticradiation to generate a cationic species which initiates curing of theoligomer (which compounds are hereinafter referred to for convenience as"photo sensitive cationic initiators") and hence causes curing thereofto form a cured resin.

Photo-sensitive cationic initiators are well known in the art, see forexample Journal Macromolecular Science, Reviews in MacromolecularChemistry, 1981-82, C21, pages 238-39. As examples thereof we wouldmention inter alia diaryl iodonium salts, e.g. diphenyl iodoniumhexafluorophosphate and triaryl sulphonium salts, e.g. triphenylsulphonium hexafluorophosphate. The less nucleophilic the anion thefaster is the speed of polymerisation.

Oligomers of which a composition according to the first aspect of thepresent invention is comprised which have pendant and/or terminalcarboxyl groups may be reacted with a suitable co-reactant, e.g. abisepoxide or bisoxazoline, to form resins having useful properties.Alternatively, they may be converted into intermediates, e.g.oxazolines, by reaction with ethanolamine, which intermediates may bereacted with suitable co-reactants to form further useful resins. Forexample, the oxazolines may be reacted with dicarboxylic acids.

Oligomers of which a composition according to the first aspect of thepresent invention is comprised which have pendant and/or terminalhydroxymethyl groups can be cured by heating, for example to atemperature in the range 80° C. to 150° C. They have the advantage thatno acid by-products are produced during the curing process.

Oligomers of which a composition according to the first aspect of thepresent invention is comprised which have pendant and/or terminal##STR9## groups may be cured by reacting with, for example, a diamine toform a polyimide resin.

Oligomers of which a composition according to the first aspect of thepresent invention is comprised which have pendant and/or terminal##STR10## groups may be cured by reaction with, for example, a suitableformaldehyde-source, e.g. hexamethylene tetra-amine or, for the terminalamino oligomer, a suitable anhydride, e.g. pyromellitic anhydride.

Where compositions according to the present invention are used toprovide the matrices for fibre-reinforced composites suitable fibrereinforcing materials include, for example, glass, e.g. in the form ofmat, tapes, continuous fibre or chopped rovings, carbon fibre, inorganicmineral fibres and fibres of organic polymers, e.g. polyamides andpolyesters.

Where a cured resin derived from a composition of the first aspect ofthe present invention is used as a matrix for a fibre-reinforcedcomposite, such a composite may be produced for example by placing thefibres, for example carbon fibres, in a mould of the desired shape andthen impregnating the fibres with the composition. The composition maythen be allowed or caused to cure. Where the composition is a solid oris very viscous and is thus not sufficiently fluid for satisfactoryimpregnation of the fibres, the composition may be diluted with a lowboiling solvent in order to provide a mixture of the desired fluidity,the low boiling solvent being caused or allowed to evaporate before thecomposition is cured.

Compositions according to the first aspect of the present invention mayinclude inter alia heat and light stabilisers, antioxidants, colouringpigments and particulate filler materials, e.g. chalk, calciumcarbonate, talc, mica, carbon black and glass.

Where curing of compositions according to the first aspect of thepresent invention is initiated by an initiator composition, particularlya photo-initiator composition, the concentration thereof in thecomposition may be in the range 0.01% to 10% by weight. For example, forpermanent dry film resists the concentration of the photo-initiatorcomposition in the composition may be in the range 1% to 4% by weight;for dental materials the concentration of the photo-initiatorcomposition in the material may be in the range 0.1% to 1.0% by weight;and for camera speed resists the concentration of the photo-initiatorcomposition may be in the range 0.1% to 2.0% by weight.

It will be appreciated that where photo-initiator compositions are usedin the present invention that part of the preparation ofphoto-polymerisable compositions in which the photo-initiatorcomposition is added, and subsequent manipulations, e.g. preparation ofa film or paste, should be carried out in the substantial absence of theelectro-magnetic radiation to which the photoinitiator composition issensitive.

Whilst various additives, e.g. fillers, reinforcing materials or inertdiluents, may be present in the compositions according to the presentinvention which comprise photo-initiator compositions it will beappreciated that where such additives are present they are such thatthey do not unduly diminish the transparency or translucency of thecompositions. Where the transparency or translucency of the compositionis unduly diminished polymerisation thereof may be reduced or prevented.

The invention is now illustrated by the following Examples.

In the Examples:

Number average and weight average molecular weights were determined bygel permeation chromatography on a Waters Liquid Chromatograph fittedwith μ Styragel (Registered Trade Mark) columns;

Flexural properties were determined under the conditions of ASTM.

EXAMPLE 1

This example illustrates the preparation of an oligomer in which atleast a portion of the functionality is provided by formyloxymethylgroups and which can be converted into an oligomer as defined in thefirst aspect of the present invention.

Distilled diphenyl oxide (340 grams; 2.0 moles), paraformaldehyde (280grams; 9.3 moles), formic acid (1200 mls; 31.8 moles) andorthophosphoric acid (16 mls; 0.28 moles; specific gravity 1.75) weremixed, stirred and heated to 80° C. when a vigorous reaction occurred.When the reaction subsided, the resulting clear solution was refluxedfor 6 hours and allowed to cool overnight.

A white solid separated out, the mother liquors were decanted and thesolid was washed with water. It was dissolved in hot chloroform, thesolution cooled, washed with saturated NaHCO₃ until free of acid, thenwith saturated NaCl and finally dried over MgSO₄. Emulsions which formedin the washing stages were broken by filtration through celite.

Most of the solvent was removed on a rotavapour leaving a viscoustransparent liquid. This was further dried in a vacuum oven at 100° C.to leave a viscous liquid which on cooling set to a glassy solid ofsoftening point 52° C. (hot-stage microscope) (Yield 380 grams). Theglassy solid has a number average molecular weight of 1116 and a weightaverage molecular weight of 1403 (Mw/MN=1.26). The saponification valueof the glassy solid was 170 mgs KOH/gram; the functionality thereof was3.4; infra-red analysis indicated the presence of >C═O (1725 cm⁻¹),φ--O--φ (1240 cm⁻¹) and C--O ester (1170 cm⁻¹); and proton magneticresonance spectroscopy (in deuterochloroform) indicated the presence ofcarboxylic H (8 ppm; singlet), aromatic protons (7 ppm; multiplet),AR-CH₂ OCOH (5.2 ppm; multiplet) and O--φ--CH₂ --φ-- (3.9 ppm; singlet).

EXAMPLE 2

This example illustrates the preparation of an oligomer which can beconverted into an oligomer as defined in the first aspect of the presentinvention.

The procedure of Example 1 was repeated except that 250 grams (8.3moles) of paraformaldehyde were used instead of 280 grams and 25 mls(0.43 moles) of orthophosphoric acid were used instead of 16 mls.

The product was a glassy solid (Yield 445 grams) of softening point 60°C. The product had a number average molecular weight of 1519 and aweight average molecular weight of 2432 (Mw/MN=1.52) and thefunctionality was found to be 4.2.

EXAMPLES 3-12

These examples (except Example 12) illustrate the preparation ofoligomers as defined in the first aspect of the invention in which atleast a portion of the functionality is provided by acetoxymethylgroups.

General Procedure

Acetic acid, water and 85% w/w sulphuric acid were added toparaformaldehyde and stirred to form a homogeneous solution which washeated to 78° C. Molten diphenyl oxide was added dropwise over severalminutes to the hot solution whilst the temperature thereof was keptbelow 80° C. The reaction mixture was stirred at 78° C. and a whitecloudy emulsion and/or a slurry formed. The hot reaction mixture waspoured into a mixture of cold water (2 liters) and methylene chloride(500 mls). The resulting mixture was stirred for 15 minutes, the layerswere allowed to separate, the aqueous layer was decanted off and theorganic layer was washed with 10% bicarbonate solution and then withwater until neutral. The organic layer was dried overnight overmagnesium sulphate and the methylene chloride was evaporated on a rotaryevaporator to leave a clear pale yellow viscous gum or a pale yellowbrittle solid.

The reaction conditions and the characteristics of the products aregiven in Table 1. Proton magnetic resonance and infra-red spectroscopyconfirmed the structures of the oligomers.

EXAMPLE 13

This example illustrates an oligomer as defined in the first aspect ofthe present invention in which there are trifluoroacetoxymethyl pendantand/or terminal groups and use of a portion of the carboxylic acid asthe strong acid in the preparation thereof.

                                      TABLE 1                                     __________________________________________________________________________    Reaction Conditions                  Product                                      Diphenyl                                                                           Formal-                                                                            85%   Acetic       Yield  Number of                                                                              Number of                    Ex- Oxide                                                                              dehyde.sup.a                                                                       Sulphuric                                                                           Acid                                                                              Water                                                                             Time (in    Acetoxy Groups                                                                         Hydroxy                                                                                Function-           ample                                                                             (moles)                                                                            (moles)                                                                            Acid (mls)                                                                          (mls)                                                                             (mls)                                                                             (Hours)                                                                            (grams)                                                                           M.sub.n                                                                          per Molecule.sup.b                                                                     per Molecule.sup.c                                                                     ality               __________________________________________________________________________    3   0.27 2.10 150   450 69  0.33 41  1324                                                                             4.2      1.7      5.9                 4   0.17 0.70  50   150 23  0.5  32  1116                                                                             3.3      0.6      3.9                 5   0.15 0.23  25    75 115 3    .sup.d                                                                            910                                                                              2.3      0.4      2.7                 6   0.47 0.51 130   360 0   1    146 630                                                                              1.0      0.2      1.2                 7   0.93 1.63 176   530 80  2    280 820                                                                              1.8      0.3      2.1                 8   0.825                                                                              6.3  450   1350                                                                              270 0.33 98  1679                                                                             4.4      2.2      6.6                 9   0.457                                                                              0.69  73   225 34.5                                                                              2    76  892                                                                              3.3      0.3      3.6                 10  0.825                                                                              6.3  450   1350                                                                              2.70                                                                              0.33 176 1101                                                                             4.7      0.5      5.2                 11  0.453                                                                              0.69  73   225 34.5                                                                              2    96  919                                                                              3.8      .sup.d   .sup.d              12  0.23 0.304.sup.e                                                                         2     5      2    46  975                                                                              2.5      .sup.d   .sup.d              __________________________________________________________________________     .sup.a Used in the form of paraformaldehyde                                   .sup.b Determined by hydrolysis of the acetoxy groups with 0.5 M potassiu     hydroxide in 2methoxy-ethanol                                                 .sup.c Determined by acetylation with acetic anydride/acetic acid solutio     .sup.d Not determined                                                         .sup.e 37% formaldehyde                                                  

Trioxan (8 grams; 267 milimoles) was added to a stirred solution ofdiphenyl oxide (11.34 grams; 67 milimoles), trifluoroacetic acid (51mls; 667 milimoles) and trifluoroacetic anhydride (9.4 mls; 67milimoles) in dichloromethane (250 mls; 3.17 moles). The reactionmixture was refluxed for 30 minutes under nitrogen then poured intosodium bicarbonate solution. The product was extracted into chloroformand recovered from the chloroform by dropwise addition of methanol.

The product (8.0 grams) was found by GPC, to have Mn of 6800, and Mw of18,829. DSC indicated a softening point of 152° C. and quantitative C¹³nuclear magnetic resonance spectroscopy indicated that the ratio ofparapara to ortho-para linkages was 2:1.

EXAMPLES 14-16

These examples illustrate oligomers as defined in the first aspect ofthe present invention which have methacrylyloxymethyl pendant and/orterminal groups.

Diphenyl oxide was added over 1-2 minutes to a clear solution of 98%sulphuric acid, water, paraformaldehyde and methacrylic acid (containing100 ppm hydroquinone and 100 ppm Topanol O) at 60° C. The reactionmixture was well stirred and the temperature thereof was maintained at60°-75° C.

After 1.25 hours, less than 1% of the diphenyl ether was unreacted, asshown by GLC. The reaction mixture was allowed to separate into twolayers, the upper organic layer was recovered and Topanol (2 grams) wasadded thereto. The organic layer was washed with hot (60° C.) water (3×8liters) and a viscous white liquid was obtained. The liquid wasdissolved in methylene chloride, the resulting solution was washed withsaturated sodium bicarbonate solution, dried over magnesium sulphate andthe solvent was removed on a rotavapour to leave a pale yellow viscousliquid.

                                      TABLE 2                                     __________________________________________________________________________    Reaction Conditions             Product                                       Ex-                   Meth-                                                                              Reaction          Number of                                                                            Number                                                                              Topanol             am-                                                                              Diphenyl                                                                           Formal-                                                                            Sulphuric                                                                              acrylic                                                                            Tem- Yield        Methacryloxy                                                                         Hydroxy                                                                             Concen-             ple                                                                              Oxide                                                                              dehyde.sup.a                                                                       Acid.sup.b                                                                         Water                                                                             Acid perature                                                                           (Kilo-    M.sub.w /                                                                        Groups per                                                                           Groups                                                                              tration             No.                                                                              (moles)                                                                            (moles)                                                                            (moles)                                                                            (moles)                                                                           (moles)                                                                            (°C.)                                                                       grams)                                                                            M.sub.n                                                                          M.sub.w                                                                          M.sub.n                                                                          molecule                                                                             Molecule                                                                            (ppm)               __________________________________________________________________________    14 7.18 56   58.9 160 94   63   1.9 882                                                                              1348                                                                             1.53                                                                             4.20   0.60  1066                15 6.04 9.3  45.1 122 58.7 68   1.1 707                                                                               960                                                                             1.36                                                                             1.72   0.19  690                 16 7.18 66.7 58.9 160 94   75   2.1 988                                                                              1395                                                                             1.40                                                                             4.95   0.84  590                 __________________________________________________________________________     .sup.a As paraformaldehyde                                                    .sup.b 98%                                                               

Details of the reaction conditions and products are given in Table 2.

Quantitative C¹³ nuclear magnetic resonance spectroscopy indicated thatin Examples 14 and 16 the ratios of para-para linkages to ortho-paralinkages were 3.4:1 and 3.8:1 respectively.

EXAMPLE 17

This example illustrates an oligomer as defined in the first aspect ofthe present invention derived from diphenyl and diphenyl oxide.

A warm solution of diphenyl (3.5 grams; 22.5 milimoles) and diphenyloxide (5.8 grams; 22.5 milimoles) in acetic acid (7.5 mls) was added toa solution of paraformaldehyde (5.4 grams; 180 milimoles) in acetic acid(30 mls) and 98% sulphuric acid (12 mls) at 75° C. After 10 minutesstirring at 75° C., a sticky solid separated from the reaction mixture,and water and then methylene chloride were added to the reactionmixture. The oligomer was recovered from the methylene chloride as apale yellow solid (7 grams), Mn 857, (Mw/Mn) 2.5, softening point70°-115° C., functionality 1.5 acetoxymethyl groups.

EXAMPLES 18 and 19

These examples illustrate oligomers as defined in the first aspect ofthe present invention derived from diphenyl.

Diphenyl was added to a solution of paraformaldehyde in acetic acid (25mls) and 98% sulphuric acid (8 mls) at 90° C. A solid rapidly separatedfrom the reaction and within 5 minutes the reaction mixture was in theform of a yellow sticky solid. Water and then methylene chloride wereadded to the reaction mixture and the oligomer was recovered from themethylene chloride.

The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                                          Number of                                   Example                                                                              Diphenyl Formaldehyde      Acetoxy Groups                              No     (moles)  (moles)      M.sub.n                                                                            per Molecule                                ______________________________________                                        18     0.03     0.24         586  1.7                                         19     0.06     0.24         525  0.7                                         ______________________________________                                    

EXAMPLE 20

This example illustrates an oligomer as defined in the first aspect ofthe present invention derived from diphenyl and havingdichloroacetoxymethyl pendant and/or terminal groups.

Dichloroacetic acid (6.2 grams), followed by 85% w/w sulphuric acid (30grams), was added with stirring to a mixture of diphenyl (1.0 grams; 6.5milimoles) and 37% formaldehyde solution (1.1 gram; 13.6 milimoles)stirred at 45° C. A clear solution formed, within 3 minutes a productbegan to separate, and stirring was continued for 15 minutes. Thereaction was cooled, water (100 mls) was added, the product wasfiltered, washed with water (3x) and dried at 50° C. for 18 hours at 1.0mm Hg. The oligomer (1.1 gram) was obtained as a pale brown solid,softening point 120°-160° C. GPC examination of the solid indicatedM_(n) =868, M_(w) =1094 and less than 2% of unreacted diphenyl.

EXAMPLE 21

This example illustrates an oligomer as defined in the first aspect ofthe present invention derived from naphthalene and havingdichloroacetoxymethyl pendant and/or terminal groups.

Dichloroacetic acid (6 grams), followed by 85% sulphuric acid (3.0grams), was added with stirring to a mixture of naphthalene (1.0 gram;7.8 milimoles) and 37% formaldehyde solution (2.0 grams; 24.7 milimoles)at 50° C. The resulting turbid mixture was stirred at 50° C. for 35minutes and then worked up as in Example 20. The oligomer (1.1 grams)was obtained as a pale yellow solid with softening point of 80°-120° C.GPC examination of the solid indicated M_(n) =985, M_(w) =1253 and nodetectable naphthalene.

EXAMPLE 22

This example illustrates an oligomer as defined in the first aspect ofthe present invention derived from p,p'-diphenoxydi-phenyl sulphone.

A mixture of paraformaldehyde (0.10 grams), glacial acetic acid (3 mls)and 85% sulphuric acid (4.5 grams) was heated at 70° C. until a clearsolution was obtained. A solution of p,p'-diphenoxy-diphenyl sulphone(1.3 grams) in warm 1,2-dichloroethane (3 mls) was added to thesolution. The reaction mixture was stirred at 65° C. for 5.5 hours. Twoseparate liquid phases formed, which were cooled and distilled water (20mls) added thereto. The organic material was extracted into methylenechloride and the oligomer recovered therefrom as a white powder (1.2grams) of softening point 150° C., M_(n) 997 and M_(w) 1389.

EXAMPLE 23

This example illustrates an oligomer as defined in the first aspect ofthe present invention derived from p,p'-diphenoxy-benzophenone.

A solution of p,p'-diphenoxybenzophenone (1.1 grams) in1,2-dichloroethane (6 mls) was added to a homogeneous mixture ofparaformaldehyde (0.11 grams), glacial acetic acid (3.0 mls) and 85%sulphuric acid (4.2 grams) at 65° C. A clear solution was obtained whichwas stirred at 65° C. After 3 hours, the reaction mixture washeterogeneous and its viscosity had increased. After 9 hours, thereaction mixture was cooled, diluted with water and extracted withmethylene chloride. The oligomer was obtained as a dark brown solid (1.1grams) of M_(n) 1120 and M_(w) 1506. containing about 3% of unreactedp,p'-diphenoxybenzophenone.

EXAMPLES 24-27

Examples 25 and 27 illustrate the preparation of oligomers as defined inthe first aspect of the present invention having hydroxymethyl pendantand/or terminal groups.

General Procedure

Oligomers having functionality provided by formoxymethyl oracetoxymethyl groups, potassium hydroxide, and 2-methoxyethanol wererefluxed to form a brown solution which was allowed to cool and thenpoured into cold water (2 liters) when a pale yellow solid precipitated.This was filtered and the resulting "tacky" solid washed thoroughly withwater, it was then pumped dry in a vacuum-oven at 60° C. and theresultant cake ground in a mortar and pestle. The ground solid was addedto methanol (2 liters) with stirring and a sticky solid formed. This wasfiltered, pumped partially dry in a vacuum-oven, ground and dried in avacuum-desiccator over silica gel to give a pale cream solid.

Infra-red analyses of the products indicated the presence of --OH groups(broad absorbance at 3380 cm¹) and the absence of ester and carbonylgroups; and proton magnetic resonance spectroscopy indicated thepresence of aromatic protons (7 ppm; multiplet), --CH₂ OH (4.6 ppm;broad doublet), --φ--CH₂ --φ-- (3.9 ppm; singlet) and hydroxyl (2.8 ppm;broad singlet which disappears on shaking with D₂ O). Othercharacteristics of the products, and the reaction conditions employedfor the preparation thereof are given in Table 4.

EXAMPLES 28-31

These examples illustrate oligomers as defined in the first aspect ofthe present invention having carboxyl pendant and/or terminal groups.

General Procedure

Jones reagent (prepared from chromic acid (85 grams), water (248 mls)and concentrated sulphuric acid (72 mls)) was added slowly with stiringto an acetone suspension of oligomer in which the functionality isprovided by hydroxymethyl groups. A vigorous reaction ensued the acetonerefluxed and a thick green solid precipitated out of solution. Themixture was stirred and refluxed for 1.5 hours and then cooled toambient temperature.

A yellow brown solution separated out above a green oily layer. Thesolution was decanted, concentrated to approximately 1 liter and thenpoured into approximately 3 liters of water with stirring. A pale creamsolid precipitated, which was filtered, washed with water and dried in avacuum-oven at 80° C. and then in a vacuum-desiccator over silica gel togive a pale cream solid. Infra-red analysis indicated the presence of OH(3200 cm⁻¹ ; broad) and carbonyl (1690 cm⁻¹) and proton magneticresonance (in D6-acetone) indicated the presence of ##STR11##

                                      TABLE 4                                     __________________________________________________________________________    Reaction Conditions       Product                                                  Precursor                                                                           Weight of                                                                           Wt of                                                                              Reflux              Softening                                Prepared                                                                            Precursor                                                                           KOH  Time                                                                              Yield           Point.sup.b                         Example                                                                            in Example                                                                          (grams)                                                                             (grams)                                                                            (hours)                                                                           (grams)                                                                            M.sub.n                                                                          Functionality.sup.a                                                                   (°C.)                        __________________________________________________________________________    24   1     220   50   1   180  1126                                                                             3.6     80                                  25   2     400   103  2   310  1473                                                                             4.2     92                                  26   7     126   16   1   104   743                                                                             2.4     55                                  27   8      77   13   1    66  1494                                                                             6.7     85                                  __________________________________________________________________________     .sup.a Determined by acetylation with acetic anhydrode/acetic acid            solution                                                                      .sup.b Determined on a hotstage microscope    (8.0 ppm; broad doublet),       aromatic protons (7.0 ppm; broad multiplet) and --φ--CH.sub.2     --φ-- (3.9 ppm; singlet).

Details of the reaction conditions and further characteristics of theproducts are given in Table 5.

EXAMPLES 32-38

These examples illustrate oligomers as defined in the first aspect ofthe present invention having carboxyl pendant and/or terminal groups andin-chain keto groups.

General Procedure

Oligomer (10 grams) was dissolved in pyridine (500 mls) and water (250mls) was added with stiring; partial precipitation of the oligomer withformation of an emulsion occurred. Potassium hydroxide (10 grams) andpotassium permangamate (25 grams) were added to the emulsion and themixture was stirred at 80° C. for 8 hours. Equal weights of potassiumhydroxide and potassium permangamate were added, where required, duringthe reaction to maintain the pH of the reaction mixture above 7 and thecolour thereof purple. Water (250 ml) was added to the reaction and thereaction mixture was filtered. The solid residue was washed with dilutepotassium hydroxide solution and then several times with water. Thecombined washings and filtrate were acidified with hydrochloric acid,and a white solid was precipitated which was filtered, washed thoroughlywith water and dried under vacuum at 60° C.

Traces of pyridine associated with the products were removed byconverting the carboxyl groups of the products into sodium salts, andazeotroping with water until no pyridine was detected in the distillate(by UV). The free acids were regenerated and dried.

                                      TABLE 5                                     __________________________________________________________________________    Reaction Conditions          Product                                               Precursor                                                                           Weight of                                                                           Jones                                                                              Temp-                    Softening                           Prepared                                                                            Precursor                                                                           Reagent                                                                            erature                                                                           Time                                                                             Yield  Function-                                                                          Equivalent                                                                          Point.sup.c                    Example                                                                            in Example                                                                          (gms) (mls)                                                                              (°C.)                                                                      (hrs)                                                                            (gms)                                                                             M.sub.n                                                                          ality.sup.a                                                                        Weight.sup.b                                                                        (°C.)                   __________________________________________________________________________    28   24    100   150  20  16 46.8                                                                              1170                                                                             3.6  326   135                            29   25    100   320  50  1.5                                                                              52.5                                                                              1532                                                                             4.3  358   145                            30   26     50   105  20  16 34.2                                                                               760                                                                             1.7  447    78                            31   27     60   240  50  1  38.2                                                                              1587                                                                             6.4  248   175                            __________________________________________________________________________     .sup.a Determined by titration against alcoholic potassium hydroxide          ##STR12##                                                                     .sup.c Determined on a hotstage microscope                               

Infra-red analyses of the products indicated the presence of carboxylgroups (1690 cm⁻¹) and in-chain keto groups (1640 cm⁻¹) and the absenceof ester groups (no absorption at 1730 cm⁻¹). Proton magnetic resonanceanalyses of the products indicated the presence of aromatic protons(0-10 ppm) and the absence of aliphatic protons.

The products are generally soluble in tetrahydrofuran, dioxan,methoxyethanol, dimethyl sulphoxide and pyridine and generally insolublein chloroform, methylene chloride, toluene and acetone.

Details of the products are given in Table 6. Yields can be improved byusing sulphur dioxide instead of hydrochloric acid in the neutralisationstep.

                  TABLE 6                                                         ______________________________________                                                Precursor                   Softening                                         Prepared  Yield     Equivalent                                                                            Point.sup.a                               Example in Example                                                                              (%)       Weight  (°C.)                              ______________________________________                                        32      6         50        876      75                                       33      5         55        322     107                                       34      4         60        239     115                                       35      3         30        252     121                                       36      1         85        358     110                                       37      7         70        320     .sup.b                                    38      8         55        321     .sup.b                                    ______________________________________                                         .sup.a Determined by differential scanning calorimetry                        .sup.b Not determined                                                    

EXAMPLE 39

This example illustrates an oligomer as defined in the first aspect ofthe present invention in which phenolic pendant and/or terminal groupsare present.

A sample (1.55 grams) of the resin prepared in Example 12, phenol (0.304grams) and p-toluene-sulphonic acid (0.052 grams) were heated at 65° C.for 3 hours. A clear mobile melt was obtained and acetic acid wasevolved. Vacuum was slowly applied to the melt and its temperature wasraised to 80° C. After a total reaction time of 4.5 hours the melt wascooled, and a glassy pink solid formed which was dissolved in 3N causticsoda solution (15 mls). The solution was filtered, and acidified withhydrochloric acid. The precipitate which formed was extracted intochloroform. The chloroform solution was washed with water until neutral,dried over sodium sulphate and evaporated at 50° C. under vacuum. Theoligomer was obtained as a solid (1.3 grams), softening point 50°-110°C. and Mn 1040. No free phenol was detected by GPC and no carbonylgroups were detected by infra-red spectroscopy.

EXAMPLE 40

This example illustrates an oligomer as defined in the first aspect ofthe present invention in which amino pendant and/or terminal groups arepresent.

A sample (7.3 grams) of the hydroxymethyl oligomer prepared in Example24 and aniline (10 mls) were heated to 90° C. under nitrogen. 45% Borontrifluoride etherate (0.2 mls) was added and the reaction mixture washeated to 170° C. After 5 hours, proton magnetic resonance spectroscopyindicated the absence of hydroxymethyl groups. The reaction mixture wascooled, methanol (100 mls) was added and the product precipitated. Theoligomer (7.8 grams) had a softening point of 90° C., M_(n) 1096, M_(w)1462.

EXAMPLES 41-43

These examples illustrate cured resins according to the sixth aspect ofthe present invention derived from oligomers having acetoxymethylpendant and/or terminal groups.

Boron trifluoride etherate was added to a solution of oligomer inchloroform or methylene chloride. The chloroform was removed undervacuum at 40° C. and a sample of the residue was cured at 140° C., and20,000 psi for 30 minutes to give resins in the form of plaques. Themechanical properties of the resins are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Oligomer        Weight                                                        Ex-Source           of                    Soft-                               am-Exam-            Cata-   Flexural                                                                             Flexural                                                                             ening                               pleple  Weight      lyst    Modulus                                                                              Strength                                                                             Point                               NoNo    Solvent (grams)                                                                           (grams) GN/m.sup.2                                                                           MN/m.sup.2                                                                           (°C.)                        ______________________________________                                        4110    CHCl.sub.3 50                                                                             0.37    2.6    87     75.sup.b                            4211    CHCl.sub.3 10                                                                             0.10    2.2    82     .sup.a                              4317    CH.sub.2 Cl.sub.2 2                                                                       0.02    .sup.a .sup.a 120.sup.cd                          ______________________________________                                         .sup.a Not determined                                                         .sup.b By TMA                                                                 .sup.c By DMA                                                                 .sup.d Post-cured at 80° C. for 24 hours and 150° C. for 16     hours.                                                                   

EXAMPLES 44-45

These examples illustrate cured resins according to the sixth aspect ofthe present invention derived from oligomers having methacrylyloxymethylpendant and/or terminal groups.

A portion (10 grams) of the oligomer prepared in Example 14 was warmedto 50° C. and catalyst (0.1 gram) was added. Samples of the mixture werecured at:

A. 85° C. for 18 hours,

B. 85° C. for 18 hours then 140° C. for 18 hours.

The mechanical properties of the cured samples are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                   Cure Cycle A                                                                              Cure Cycle B                                                            Flexural Flexural                                                                             Flexural                                                                             Flexural                              Example          Strength Modulus                                                                              Strength                                                                             Modulus                               No.    Catalyst  MPa      GPa    MPa    GPa                                   ______________________________________                                        44     Benzoyl   62.5     2.93   121    3.90                                         peroxide                                                               45     t-Butyl   98.5     3.41   120    3.73                                         per (2-                                                                       ethyl)                                                                        hexanoate                                                              ______________________________________                                    

EXAMPLES 46-59

These examples illustrate the preparation of cured resins from oligomersas defined in the first aspect of the present invention.

Mixtures of oligomers as defined in the first aspect of the presentinvention in which the functionality is provded by carboxyl groups andepoxy resins of bisphenol-A-epichlorohydrin (Epikote (RTM), ex ShellChemicals) were prepared as follows:

Heat Mixing

Oligomer and epoxy resin containing equivalent amounts of carboxylgroups and epoxy groups (except where indicated) were heated together atabout 170° C. for 5-10 minutes and stirred with a spatula. Thecomponents were well mixed. The mixture was cooled and the resultingsolid was ground to a powder.

Solution Mixing

Oligomer and epoxy resin containing equivalent amounts of carboxylgroups and epoxy groups were dissolved in tetrahydrofuran to give aclear solution. The tetrahydrofuran was removed by vacuum distillationand the resulting powdery foam was dried overnight at about 75° C. underhigh vac.

The mixtures were moulded at 120°-180° C. for 5-30 minutes at 1000 psi.

The moulded samples were cured in four stages, each of four hours, at125° C., 150° C. 175° C. and 200° C.

Details of the reagents used and the properties, softening points anddynamic mechanical analyses, of the products are given in Table 9.

                                      TABLE 9                                     __________________________________________________________________________                     Product                                                                       Glass                                                        Oligomer   Epikote                                                                             Transition                                                                          Young's Modulus                                                                            Flexural Tests                            Prepared   Reference                                                                           Temp- (GPa)        Modulus                                                                            Strength                             Example                                                                            in Example                                                                          Number                                                                              erature.sup.d                                                                       -50° C.                                                                     20° C.                                                                     100° C.                                                                    (GPa)                                                                              (MPa)                                __________________________________________________________________________    46   37    828   144   2.7  2.3 2.0 2.1  46                                   47   38    1007  115   2.0  1.6 1.3 2.3  83                                   48   38    828   166   3.2  2.6 2.3 2.2  54                                   49   38    1007  113   2.3  1.8 1.5 2.0  43                                   50   .sup. 38.sup.b                                                                      828   146   3.2  2.8 2.2 2.5  73                                   51   .sup. 38.sup.c                                                                      828   162   3.2  2.8 2.3 2.2  64                                   52   .sup. 38.sup.a                                                                      828   170   2.4  2.0 1.6 2.5  80                                   53   34    1004  120   3.7  3.0 2.5 2.4  78                                   54   34    828   170   3.2  2.8 2.3 2.9  110                                  55   30    828   100   2.5  2.2 0.2 2.8  79                                   56   30    1007  110   2.9  2.4 1.6 2.3  80                                   57   31    828   206   2.9  2.5 2.1 2.5  50                                   58   31    1007  124   2.5  2.0 1.6 2.3  75                                   59   28    1004  150   2.7  2.4 1.9 2.9  105                                  __________________________________________________________________________     .sup.a Mixture was prepared by solution mixing; mixtures of the other         Examples were prepared by heat mixing                                         .sup.b Half the molar equivalent of acid was used                             .sup.c Three-quarters of the molar equivalent of acid was used                .sup.d Determined by DMA.                                                

We found that the carboxyl-functionalised oligomers in which there weremethylene groups in the polymer backbone gave better mixtures with epoxyresins that the equivalent oligomers in which keto groups were presentin the backbone.

EXAMPLES 60-66

These examples illustrate the preparation of cured resins from oligomersas defined in the first aspect of the present invention.

Equivalent amounts of oligomers as defined in the first aspect of thepresent invention in which the functionality is provided by carboxylgroups and m-phenylenebis(2-oxazoline) or p-phenylenebis(2-oxazoline) oran equimolar mixture thereof were ground together in a micro-mill for 2hours. (The m-phenylenebis(2-oxazoline) and thep-phenylenebis(2-oxazoline) and the p-phenylenebis(2-oxazoline) wereprepared by dehydration with oleum ofN,N'-bis(2-hydroxyethyl)isophthalamide andN,N-bis(2-hydroxyethyl)-terephthalamide respectively as described inUnited Kingdom Patent Specification No. 1,468,874). The resulting powderwas pressed in a 6×1 cm piston mould between sheets of Melinex at atemperature of 150°-190° C. and a pressure of about 1000 psi for upto 1hour.

The clear brown moulding produced was cured further in a vacuum oven at90° C. for 1-2 hours, followed by further heating at atmosphericpressure and temperatures up to 190° C. for 2 hours. Infra-red analysisof the product indicated the presence of ester (1710 cm⁻¹) and amide(1650 and 1540 cm⁻¹) linkages.

Details of the reactants and products are given in Table 10.

In a comparative test an epoxy resin, Epikote EP 1001 (RTM; ex ShellChemicals) (10 grams) and phthalic anhydride (3 grams) were mixed at130° C., cast to form a plaque which was then post-cured. The propertiesof the product are shown in Table 10.

From Table 10 it can be seen that the resins of the present inventionhave a higher softening point and maintain their strength at highertemperatures than a commercially available resin.

EXAMPLE 67

This example illustrates the preparation of composites from oligomers asdefined in the first aspect of the present invention.

Boron trifluoride etherate (700 microliters) was added with stirring toa portion (130 mls) of a solution prepared by dissolving a portion (72grams) of the resin prepared in Example 9 in dry chloroform (240 mls).Carbon fibre was immersed in the mixture, removed therefrom and dried ina current of warm filtered air for 5 minutes. This was repeated untilthe carbon fibre was coated with an equal weight of thecatalyst/oligomer mixture to form a so-called "pre-preg". The pre-pregwere dried under a vacuum of 0.1 mm Hg for 18 hours at room temperature.

Layers of the pre-pregs were laid in parallel in a mould and cured at140° C. and 20,000 psig for 1 hour, and then post-cured at 104° C. for18 hours. The mechanical properties of the post-cured composites weredetermined in transverse flexural tests and short beam shear tests. Theresults are shown in Table 11.

EXAMPLE 68

This example illustrates a dental composition according to the presentinvention.

                                      TABLE 10                                    __________________________________________________________________________                                            Product                               Reaction Conditions                     Dynamic Mechanical                                      Weight                                                                              Press   Post-Curing                                                                           Analysis                                                Ratio of                                                                            Conditions                                                                            Conditions                                                                            Glass                                 Oligomer          Oligomer                                                                            Temp-   Temp-   Transition  Flexural Properties             Prepared    to    erature                                                                           Time                                                                              erature                                                                           Time                                                                              Temper-                                                                             E.sub.20.sup.a                                                                   E.sub.100.sup.b                                                                  Modulus                                                                            Strength             Example                                                                             in Example                                                                          Oxazoline                                                                           Oxazoline                                                                           (°C.)                                                                      (hour)                                                                            (°C.)                                                                      (hour)                                                                            ature (°C.)                                                                  GPa                                                                              MPa                                                                              MPa  GPa                  __________________________________________________________________________    60    28    A     3.0   130 0.5  80 2   172   2.96                                                                             2.65                                                                             3.8  109                                                  170 4                                                                         190 2                                         61    28    C     3.0   130 0.5  80 2   165   2.4                                                                              2.1                                                                              3.2  82                                                   170 2                                         62    28    B     3.0   130 0.5 100 1   172   2.32                                                                             2.15                                                                             2.9  95                                                   170 2                                         63    30    A     4.1   180 1   100 1   120   2.1                                                                              1.04                                                                             3.1  46                                                   190 4                                         64    31    A     2.3   180 0.5 100 1   158   2.7                                                                              2.35                                                                             3.2  85                                                   170 4                                         65    36    A     3.0   180 0.5  80 2   150   2.73                                                                             2.18                                                                             3.0  58                                                   190 2                                         66    29    A     3.3   195 1    90 1   165   3.23                                                                             2.85                                                                             3.2  83                                                   180 2                                         CT                              200 2   125   1.86                                                                             1.37                                                                             3.0  130                  __________________________________________________________________________     CT: Comparative test                                                          A: phenylene bis(2oxazoline)                                                  B: phenylene bis(2oxazoline)                                                  C: A mixture of A and B in ratio of 1:1                                       .sup.a Young's modulus at 20° C.                                       .sup.b Young's modulus at 100° C.                                 

                  TABLE 11                                                        ______________________________________                                        Transverse Flexural                                                           Test (Strength Values)                                                                        Short Beam Shear                                              MPa             Test (Strength Values)                                        After storing       MPa                                                       24 hours After 24   After storing                                                                              After 36 hours                               at room  hours in   24 hours at  in boiling                                   temperature.                                                                           boiling water                                                                            room temperature                                                                           water.                                       ______________________________________                                        46       40         54           41                                           ______________________________________                                    

A portion (25.68 grams) of the oligomer prepared in Example 14, bariumborosilicate glass (Raysorb T3000, ex Owens, Ill.; 74.0 grams),camphorquinone (195 mgs) and N,N-dimethylaminoethyl methacrylate (130mgms) were thoroughly mixed to give a composition which had aconsistency typical of a dental composite.

A sample of the composition was polymerised by exposure to light of peakintensity at 470 nanometers and output 1000 watts/meters² (at 470±10nanometers) for 60 seconds.

The polymerised product had a flexural strength of 75.3±7.4 MPa and aflexural modulus of 8.07 GPa.

EXAMPLE 69

This example illustrates a dental composition according to the presentinvention.

A portion (9.72 grams) of the oligomer prepared in Example 14,triethyleneglycol dimethacrylate (SR 205, ex Ancomer Chemicals; 6.08grams), barium borosilicate glass (as described in Example 68; 84.0grams), camphorquinone (120 mgms) and N,N-dimethylaminoethylmethacrylate (80 mgms) were thoroughly mixed to give a composition whichhad a consistency typical of a dental composite. The ratio of oligomerto triethylene glycol dimethacrylate was such that the organic componentof the composition had a refractive index of 1.553, which was the sameas that of the glass.

A sample of the composition was polymerised under the conditionsdescribed in Example 68.

The polymerised product had a flexural strength of 97.6±13.0 MPa and aflexural modulus of 16.44±1.16 GPa.

EXAMPLE 70

This example illustrates an oligomer as defined in the first aspect ofthe present invention having methacrylyloxymethyl pendant and/orterminal groups.

The procedure described in Example 14 was repeated except that 28 molesof paraformaldehyde were used instead of 56 moles.

Gel permeation chromatography revealed that oligomer had a M_(n) of 763and a M_(w) of 1127.

The number of methacrylyloxy groups per molecule of oligomer was foundto be 2.87 and the number of hydroxy groups per molecule of oligomer wasfound to be 0.45.

Quantitative C¹³ nuclear magnetic resonance spectroscopy indicated thatthe ratio of para-para linkages to ortho-para linkages was 4.7:1.

EXAMPLE 71

This example illustrates an oligomer useful as a permanent dry filmresist according to the present invention.

The general procedure described in Examples 3-12 was repeated usingparaformaldehyde (10.5 grams; 0.35 moles), diphenyl oxide (24.4 mls;0.15 moles), water (11.5 mls), glacial acetic acid (75 mls) and 85%sulphuric acid (25 mls), and the reaction was carried out for 2 hours at78° C.

The product had a M_(n) of 1150, a (M_(w) /M_(n)) of 1.5, and afunctionality of 4.4 (number of acetoxy groups per molecule=3.1; numberof hydroxy groups per molecule=1.3).

EXAMPLE 72

This example illustrates an oligomer as defined in the first aspect ofthe present invention which has acrylyloxymethyl pendant and/or terminalgroups.

A mixture of distilled water (28.8 grams; 1.6 moles), 98% sulphuric acid(58.9 grams; 0.6 moles) and paraformaldehyde (8.4 grams; 0.26 moles) wasstirred and heated at 70° C. until a clear solution formed. Acrylic acid(84 grams; 1.17 moles), containing p-methoxyphenol (0.07 grams; 830 ppmbased on acrylic acid) was added to the clear solution and thetemperature was adjusted to 65° C., diphenyl oxide (12.2 grams; 0.072moles) was then added over a period of 5 minutes while the temperaturewas kept below 70° C. The reaction mixture rapidly became opaque.

After a total reaction time of 30 minutes the reaction mixture waspoured, with stirring, into cold distilled water (300 cc). The mixturewas allowed to settle, the supernatant aqueous layer was decanted andthe crude oligomer was washed with water (200 cc×2), and then dissolvedin methylene chloride. The methylene chloride solution was washedrepeatedly with water, dried over a molecular sieve and the solvent wasremoved under vacuum at 40° C. The oligomer was obtained as a semi-solid(12.8 grams); gel permeation chromatography indicated M_(n) =932, andM_(w) =1198; and the functionality was 3.4.

EXAMPLE 73

This Example is a comparative example which illustrates an oligomerknown in the art.

Example 40 of U.S. Pat. No. 3,914,194 was repeated. Diphenyl oxide (8.5grams), paraformaldehyde (4.47 grams), methacrylic acid (18.9 cc),p-toluene-sulphonic acid (0.95 grams) and p-methoxyphenol (0.6 grams)were heated at reflux for 90 minutes. To avoid polymerisation ofmethacrylic acid, it was found necessary to add further amounts (0.01grams×3) of p-methoxyphenol during the reaction. The reaction mixturewas poured into water (150 cc), and an oil was decanted and washed withwarm water, dilute ammonia solution, and warm water (2x). The stickyviscous liquid which was obtained was dissolved in methylene chloride,dried over a molecular sieve, filtered and stipped at 50° C. under vac.

A pale straw viscous liquid (10.8 grams) was obtained; gel permeationchromatography indicated M_(n) =1160 and M_(w) =1929; quantitative C¹³-nuclear magnetic resonance spectroscopy indicated that the ratio ofpara-para linkages to ortho-para linkages was 6.3:1.

A sample of the product, containing 2% w/w N,N-dimethyl-2-aminoethylmethacrylate and 1% w/w camphorquinone cured in daylight inapproximately 5 minutes and was still soft and flexible after 24 hours.Under the same curing conditions a sample of the oligomer prepared inExample 14 cured in less than 30 seconds and was hard and rigid after 24hours.

EXAMPLE 74

This Example illustrates the preparation of an oligomer of highmolecular weight according to the present invention.

A mixture of diphenyl oxide (42.5 grams), methacrylic acid (130 mls),85% w/w sulphuric acid (67.6 mls) and water (20 mls) was heated to 65°C. and solution of trioxane (30 grams) in methacrylic acid (50 mls) wasadded portionwise over 30 minutes. The temperature rose to 70° C. duringthe addition. The reaction mixture was heated for a further 2.5 hours at65° C.

The reaction mixture was worked up as in Example 71 to leave an oligomeraccording to the present invention in the form of a tack-free glass (50grams); gel permeation chromatography indicated M_(n) =1850 and M_(w)=9000; the functionality was 5.9 and C¹³ nuclear magnetic resonancespectroscopy indicated as ratio of para-para linkages to ortho-paralinkages.

EXAMPLES 75-82

The procedure described in Example 74 was repeated using the molarratios shown in Table 12 for the times and with the results indicatedtherein.

                  TABLE 12                                                        ______________________________________                                        Ex-                                                                           am-  Molecular            Reaction       Func-                                ple  Ratios               Time           tion-                                No.  AB      C      D    E    (Hours)                                                                              M.sub.w                                                                            M.sub.n                                                                            ality                          ______________________________________                                        75   12.26   2.2    8.00 1.50 1.00   4500 2500 2.4                            76   11.80   3.1    8.80 1.60 1.75   1833 1027 2.2                            77   13.95   9.7    8.24 2.64 2.50   1271  870 2.8                            78   13.95   10.5   8.48 3.33 3.00   1264  849 2.9                            79   13.95   9.6    8.48 3.33 2.75   1274  875 2.6                            80   12.26   4.4    8.48 3.33 2.50   1310  898 2.3                            81   12.70   4.9    8.48 4.00 2.00   1334 1017 2.9                            82   13.38   7.7    8.48 4.00 2.10   2568 1078 3.4                            ______________________________________                                         A: Diphenyl oxide                                                             B: 85% w/w sulphuric acid                                                     C: Water                                                                      D: Methacrylic acid                                                           E: Formaldehyde (in the form of trioxan)                                 

The ratio of para-para linkages to ortho:para linkages was found to be3.1:1 in Example 82.

EXAMPLE 83

The general procedure described in Examples 14-16 was repeated usingdiphenyl oxide (1.14 liters), paraformaldehyde (1.8 kilograms),methacrylic acid (8 liters) and sulphuric acid (specific gravity 1.550;6 liters). The reaction was stopped after 2.75 hours.

The product had M_(n) =878; a functionality of 4.2; and apara-para:ortho-para ratio of 4.5:1.

EXAMPLE 84

The general procedure described in Examples 14-16 was repeated usingdiphenyl oxide (28.5 mls), trioxan (22.5 grams), methacrylic acid (200mls), sulphuric acid (specific gravity 1.550; 150 mls) and water (80grams). The reaction was stopped after 21 hours.

The product had a ratio of para-para linkages to ortho-para linkages of4.2:1.

EXAMPLE 85

This Example illustrates the good wear properties of a dentalcomposition according to the present invention.

A dental composition according to the present invention, comprising apreferred three component initiator system, and prepared by thoroughlymixing a portion (64.0 grams) of the oligomer prepared in Example 14,triethylene glycol dimethacrylate (59.1 grams), a borosilicate glasshaving the particle size distribution indicated in FIG. 2 of U.S. Pat.No. 4,407,984 (428 grams), camphorquinone (0.93 grams),N,N-dimethyl-2-aminoethyl methacrylate (0.63 grams) and t-butylperbenzoate (1.23 grams) was cured under the conditions described inExample 68.

The cured product had a flexural strength of 101.1±10.1 MPa, a flexuralmodulus of 12.9±0.7 GPa and a wear depth of 41.8±7.4 microns on an areaof 0.191 mm² as determined by the method described in the Journal ofBiomedical Materials Research (1975), Volume 9, pages 341-353 at 340,000cycles under a load of 350 grams with a cusp diameter of 3 mm at 60cycles/minute.

In a comparative test a known dental composition comprising a vinylurethane resin (58.35 grams) derived from oxypropylated-bisphenol A,hexamethylenediisocyanate and hydroxyisopropyl methacrylate as describedin U.S. Pat. No. 4,407,984, borosilicate glass as hereinbefore described(428 grams), camphorquinone (0.88 grams), N,N-dimethyl-2-aminoethylmethacrylate (0.58 grams) and t-butyl perbenzoate (1.17 grams) was curedas described in Example 68.

Under the conditions hereinbefore described it showed more wear (weardepth 47.3±20.6 microns on an area of 0.239 mm²) than the cured productfrom the dental composition according to the present invention.

I claim:
 1. A dental filling material which comprises(a) an oligomer,which may be linear or branched, which(i) comprises the repeating unit

    --Ar.sup.1 -CHR--

wherein Ar¹ is an aromatic group, or a substituted derivative thereof,each of which aromatic groups may be the same or different and R, eachof which may be the same or different, is hydrogen or a hydrocarbylgroup; (iii) has pendant and/or terminal groups, which may be the sameor different; which are acyloxymethyl groups in which the acyl portionis derived from polymerizable olefinically unsaturated carboxylic acid;and (iii) has an average functionality between 0.5 and 10; and (b) aparticulate filler.
 2. A fluid dental filling material as claimed inclaim 1 comprising a comonomer which is copolymerisable with theoligomer.
 3. A dental filling material as claimed in claim 2 wherein thecomonomer is an ester of acrylic acid or methacrylic acid.
 4. A dentalfilling material as claimed in claim 3 wherein the ester is a diester ofdiethylene glycol or triethylene glycol.
 5. A dental filling material asclaimed in claim 2 wherein the ratio of the oligomer to thecopolymerizable monomer is such that the refractive index of the mixturethereof is equal to the refractive index of the particulate filler.
 6. Adental filling material as claimed in claim 1 wherein Ar¹ has thestructure --φ--Y¹ --φ--, wherein φ is the phenylene group and Y¹ is adirect link between two phenylene groups, or a divalent residue whichincludes one or more in-chain atoms, each of which atoms may be carbonor a hetero atom and may have one or more atoms appendant thereto.
 7. Adental filling material as claimed in claim 6 wherein Y¹ is oxygen.
 8. adental filling material as claimed in claim 6 wherein the ratio ofpara-para linkages to ortho-para linkages is less than 5:1.
 9. A dentalfilling material as claimed in claim 8 in which the said ratio isbetween 5:1 and 2:1.
 10. A dental filling material as claimed in claim 1wherein R is hydrogen.
 11. A dental filling material as claimed in claim1 wherein the polymerizable olefinically unsaturated carboxylic acid isacrylic acid, methacrylic acid or both.
 12. A dental filling material asclaimed in claim 1 wherein the functionality is between 2 and
 5. 13. Adental filling material as claimed in claim 1 wherein the oligomer has anumber average molecular weight between 500 and
 1000. 14. A dentalfilling material as claimed in claim 1 wherein the particulate filler isglass.
 15. A dental filling material as claimed in claim 1 comprising aphoto-initiator system which is sensitive to visible light.
 16. A dentalproduct prepared by curing a dental filling material as claimed in claim1.